Phosphoric-acid recovery



Patented erase. rare.

I warren snares HARRY VVILIJAMS -GHARLTON, OF NEW YORK, N. Y., ASSTGNOR TO AMERICAN CYANAMID COMPANY, OF NEW YORK, N. Y., A CORPORATION OF MAINE.

PHOSPHORIC-AOID RECOVERY.

No Drawing-l To all whom it may concern:

Be it known that I, HARRY WILLIAMS CHARLTON, a citizen of Canada, residing at New'York, in the county of New York and State of New York, have invented new and useful Improvements in- Phosphoric-Acid Recovery, of which thefollowingis a specification.

This invention relatesto amethod of producing phosphoric acid in a manner similar in many respects to the methods disclosed in U. S. Patent 1,047,864, Washburn, 1912, and U. S. Patent 1,076,499, Willson and Hafl, 1913, but difiers from them in a number of essential features both as to the general conception of reaction and the details of operation.

The process about to be disclosed is essentially an electric furnace one, and requires for its proper operation, temperatures unattainable, in ordinary fuel combustion methods. On the other-"hand, a means is pointed out of avoiding the continuous maintenance of these excessive temperatures in acting on the same material for any length of time. It is suflicient to raise the temperature to the required point and maintain it there long enough for a chemical equilibrium to be established. A vital feature of thishydride which is the main product, another article of commercial value results. This is a superior grade of mineral wool suitable for use as a heat insulator both in refrigeration work and in protecting high temperature materials in pipes, etc. When manufactured by this process it may be sold at so low a price as to make it available for filling air spaces in building walls, etc., and thus retain the heat and impart sound-proof qualities. With these and other objects in view the invention consists in the various steps and'combination of steps constituting I the process and in the new product, all as Serial No. 661,523.

will be'more fully hereinafter described and particularly pointed in the claims.

As an example of the process 1000 parts of phosphate rock, .400 to 600 parts of silica usually in the formof high grade sand, and from 0 up to 250 parts of carbon, usually in the form of coke, are fused in the arc of an electric furnace. As soon as the maximum temperature has been attained and the charge is in a fluid state, it is allowed to fall in a thin stream and be disintegrated by a horizontal blast of air under high pressure. The blast under a pressure of from 75 to 100 pounds has the effect of changing the white hot liquid slagto fine grained Wool made up of a series of fine threads. The exact nature of the reaction leading up to the production. of an innumerable collection of fine threads, can only be guessed at, but it is probable that the mass of molten slag is sub-divided into 7 fine drops which. are propelled by the air blast. The friction of the air on the exterior retards the surface layer and it coalesceses into a minute thread which acts as a kind of tail to'the drop itself. During this rapid change inform the phosphoric anhydride is brought to the surface and escapes in the air currents. The slag wool settles down in the chamber and the phosphoric anhydride, in the form of a white vapor, .is carried away with the" currents of air andis deposited by electrical or other means well known in the art. v

A vital question in this process is the rate of cooling of the slag. Providing that it remains fluid through a long'range of temperature, little difliculty is met with, and the separation is very complete: In cases where the slag remains fluid through only a short range of temperature, or in cases where the. initial melting point'is very low, a slight modification is made. Instead of disintegrating the slag with an air blast, a high pressure flame may be substituted. In

this case the heat of the slag is augmented.

Thehigh pressure flame may be obtained by discharging a mixture of combustible gas and air against the slag, and so proportioning thev gases that it will correspond to what is known as either a combustible or an 1 explosive mixture.

The method of dispersing the liquid slag with a gaseous heating medium very materially extends the scope of the invention, and in certain cases makes itpossible to dispense with the preliminary electrical heating in the arc. This method is also broadly applicable to methods of-lseparating materials that are volatile at elevated temperatures from those that are not volatile.

The formation of the slag wool and the vaporization of the phosphoric anhydride is carried outin a long closed chamber, and consequently there is little loss of phosphoric acid. Of the various'methods of recovering the phosphoric anhydride probably the most satisfactory is the Cottrell process, although it may also be absorbed-in towers with hot phosphoric acid. 4

In the present invention the cost of installation of the furance is very much less than is required in' the usual processes in which. a large mass of material is melted and maintained at an elevated temperature until substantially all the phosphorus is expelled. Owing to the reduction in the time of treating, only a small amount of charge is maintained in the fluid conditionat any one time. It is only-necessary to keep enough melted to form a head for the flow of the small stream which is to be changed into wool. Consequently the process becomes a continuous one and the material is constantly fed into the arc, and the melted stream flows away continuously. This necessitates a series of small electrode units, which may either treat preheated material or fresh charge. The choice in this respect depends entirely upon the relative cost of electric energy and fuel. In regions where fuel is expensive and electric power verycheap, it

is advisable at all times to electrically melt the material from its original state, and avoid installing equipment necessary for preheating. In this case a unit consists only I comprises pneumatically dispersing a fallof a small furnace pot and a couple of electrodes, the lower electrode. preferably forming the furnace pot. Just back of the electrode is a small continuously acting feeding device, and on the other side of the arc isa small heated orifice situated so as to permit a small stream of molten material falling directly across the path of the air blast.

,of this is the formation of a glass-like stable compound of one 'molecule of silica and one molecule of phosphoric anhydride. There is every reason to believe that this compound is formed in a secondary reaction, depending largely upon an excess of the anhydride in the slag, and thatwhen the anhydride, is removed as fast as it is formed, there is little trouble in this respect.

In certain cases where objectionable side products are produced, the trouble may be overcome by adding a small amount of powdered coal, coke, charcoal, etc. This addition aids both the conductivity of the molten charge and liberates a certain amount of elemental phosphorus, which is later' oxidized by the oxygen of the blast.

It is obvious that those skilled in the art may vary the details f the process without \departing from. the spirit of the invention,

therefore I do not wish to be limited to the above disclosures except as may be required by the claims.

I claim I 1. The herein described process which comprises pneumatically dispersing a falling stream of molten material'in such a .manner that mineral threads will be formed and the whole will comprise a wool; and volatile material mechanically retained in the molten mass, will be liberated, pneumatically removed, and recovered; substantially as described.

2. The herein described process which comprises pneumaticallydispersing a falling stream of the molten material obtained by heating phosphaterock and sand in an electric furnace, in such a manner that a very large surface of the molten material will beexposed to the air currents before the threads which go to make up the wool formed by the pneumatic action, cool and solidify; substantially as described.

3. The herein described process which and powdered carbonaceous material, and

after the preliminary heating, completing the melting treatment in an electric furnace; the pneumatic dispersion being so regulated that the mineral wool formed will fall and be removed out of the path of the currents of air; and the phosphoric anhydride and elemental phosphorus will disengage themselves from the solidifying threads of molten material, and be removed in the currents of air, the phosphorus being oxidized to phosphoric anhydride; substantially as described.

4:. A process of removing phosphoric anhydride from a molten slag carrying the same which comprises blowing out the phosphoric anhydride and reducing the slag to the form of a wool; substantially as described.

5. A process of removing phosphoric anhydride from a molten slag carrying the same, which comprises bringing a stream of I falling molten slag into contact with a blast of air carrying combustible gases and thereby simultaneously' imparting heat to the slag and dispersing the same in the form of threads, and driving off the phosphoric anhydride; substantially as -described.

6. A process of removing phosphoric anhydride from a molten mass of material carrying the same which comprises disrupting the fluid into an aggregation of fine threads from which the phosphoric'anhydride is ableto escape before the threads solidify; substantially as described.

7. A process of removing phosphoric anhydride from a molten mass of phosphate rock and silica which comprises impinging upon a falling stream of the fluid with air moving at right angles and at great velocity, and permitting the threads to solidify after the removal of the phosphoric anhydride; substantially as described.

8. A method of forming slag wool and obtaining phosphoric anhydride which comprises melting a mixture of phosphate rock and sand and allowing the molten material to fall in a thin stream and be disrupted by a blast of air moving at right angles tothe molten stream, and permitting the phosphoric anhydride to escape and be carried off in the escaping air and be recovered therefrom, and allowing the fine threads of slag to settle and agglomerate to form slag wool; substantially as described.

9. A method of forming slag wool and obtaining phosphoric anhydride which comprises melting a mixture of phosphate rock and sand and allowing the molten material to fall in a thin stream and be disrupted and additionally heated by a blast of air and combustible gas,-,,and permitting the phosphoric anhydride to escape and be carried off in the outgoing gases, and allowing the slag in the form of matted hairs to settle; substantially as described.

10. A method of forming slag wool and obtaining phosphoric anhydride which comprises melting a mixtureof phosphate rock, sand and finely divided carbon, and allowing the molten material to fall in a stream and be disrupted by a blast of air moving at right angles to the stream of molten slag,

and permitting the phosphoric anhydride phoric anhydride and the elemental phosphorus and oxidizing the latter, and collecting the total phosphoric anhydride; substantially as described.

12. A method of pneumatically producing:

slag wool and recovering phosphoric anhydride which comprises disintegrating a fluld massof hosphate rock and sand and causing the s ag to assume the form of matted threads, and the phosphoric anhydride to be removed in the air currents and recovered therefrom substantially as described,

HARRY WILLIAMS CHARLTON. 

